The present invention is concerned with a process for the production of 3-hydroxypropionitrile, which is an important intermediate in the process for the manufacture of panthenol. The end product, especially its d(+) isomer, is a valuable agent for the treatment of dermatoses, burns and infectious ulcers, as well as a valuable additive in shampoos and other cosmetics.
Various methods for the production of 3-hydroxypropionitrile are known from the literature. For example, the reaction of 2-chloroethanol with an alkali cyanide to yield 3-hydroxypropionitrile (also known as xe2x80x9cethylene cyanohydrinxe2x80x9d) was described in Annalen der Chemie und Pharmacie 128, 1 (1863). Later publications, such as, for example, Org. Synth. 3, 57 (1923), J. Soc. Chem. Ind. 67, 458 (1948) and Britton et al., U.S. Pat. No. 2,311,636, concern the optimization of this basic production method. Despite the high yields allegedly achieved, the process is uninteresting commercially because of the relatively high purchase price of the 2-chloroethanol starting material, as well as the difficulty in controlling the exothermic reaction. Moreover, not only is there contamination with salt but there is also great expense involved in isolating and purifying the product of the process.
The successful production of 3-hydroxypropionitrile by the addition of hydrocyanic acid to ethylene oxide was reported around 1930 in various German patents, namely in German Patents Nos. 561,397, 570,031 and 577,686. The optimization of this addition process was described in Luskin, U.S. Pat. No. 2,653,162, in which a carboxylic acid sodium salt resin is used as the weak base, water is used as the solvent, and the reaction is effected at 45-50xc2x0 C. Still later disclosures of the production of 3-hydroxypropionitrile by the addition of hydrocyanic acid to ethylene oxide appear in German Offenlegungsschrift No. 4,304,002 as well as in Merger et al., U.S. Pat. No. 5,268,499. However, the two starting materials are very problematical with respect to toxicity and handling. Therefore, these processes would no longer be considered in developing an up-to-date production process for 3-hydroxypropionitrile.
The production of the known 1:1 addition product of water and acrylonitrile (i.e. of 3-hydroxypropionitrile) in the presence of a basic catalyst gives rise to certain difficulties since the product reacts with further acrylonitrile to give the condensation product bis(cyanoethyl)ether, NC(CH2)2O(CH2)2CN, as described in Howk et al., U.S. Pat. No. 2,579,580. Howsmon, U.S. Pat. No. 3,024,267 and Japanese Patent Publication (Kokai) No. 196,850/1984 disclose that somewhat better yields of the desired 3-hydroxypropionitrile are achieved when the reaction is carried out in a large excess of water (i.e. at high dilution) or according to J. Org. Chem. USSR 1987, 1087, in the presence of a large amount of base. However, these measures are uneconomical, especially because of the unavoidably complicated working up, the evaporation of water, and the contamination with salt. Moreover, at such high dilution, small to medium amounts of bis(cyanoethyl)ether are also formed.
The reaction of aqueous formaldehyde with acrylonitrile in the presence of strongly basic Amberlyst(copyright) IRA-400, OHxe2x88x92 form, at about 40xc2x0 C. is proposed in German Patent No. 2,655,794 as a possible solution to the above problems. However, the indicated yield of 3-hydroxypropionitrile, 75%, is moderate in this case, too.
Thus, the processes outlined above for the direct production of 3-hydroxypropionitrile have evident disadvantages.
Japanese Patent Publications (Kokai; JP) Nos. 160,949/1989, 90,160/1989, and 185,550/1983 disclose that bis(cyanoethyl)ether can be produced from acrylonitrile and water in the presence of a strong basic ion exchanger, and that the product can subsequently be pyrolyzed by means of a basic catalyst to yield the desired 3-hydroxypropionitrile and acrylonitrile. The base-catalyzed production of bis(cyanoethyl)ether from acrylonitrile and water is also known from earlier references, such as, for example, Org. Reactions 5, 79 (1945) (review article), J.A.C.S. 65, 23 (1943), J.A.C.S. 67, 1996 (1945), Ind. Eng. Chem. 44, 1388 (1952), German Patents Nos. 731,708 and 1,189,975 as well as U.S. Pat. Nos. 2,382,036, 2,448,979 and 2,816,130 to Bruson, Hopff et al., and Selcer et al., respectively. As the catalyst for this 2:1 addition reaction, a strong base (e.g. sodium hydroxide) is generally used, although a strongly basic Amberlyst(copyright) catalyst, such as Amberlyst(copyright) IRA-400, OHxe2x88x92 form, can also be used. At least small amounts of 3-hydroxypropionitrile are formed irrespective of the acrylonitrile:water ratio, the reaction temperature, or the respective strong base that is used. Based on these documents, yields of up to about 77% could be achieved using strongly basic catalysts (e.g. Amberlyst(copyright) IRA-400, OHxe2x88x92 form). The cleavage of the bis(cyanoethyl)ether described in the aforementioned Japanese patent publications is effected using a basic catalyst, especially aqueous or aqueous-methanolic potassium hydroxide/dipotassium phosphate at 72-100xc2x0 C./5 mm Hg, with about 85% yield (JP 160,949/1989, JP 90,160/1989) or tetraethylammonium acetate at 100-105xc2x0 C./10 mm Hg, with about 86% yield (JP 185,550/1983).
One aspect of the claimed invention is a process for the production of 3-hydroxypropionitrile that includes the reaction of water with acrylonitrile to give a mixture of the desired product and the bis(cyanoethyl)ether condensation product, and then the pyrolysis of this product mixture to additional 3-hydroxypropionitrile, whereby not only the mentioned reaction, but also the pyrolysis, are carried out under specific base-catalyzed and other conditions. Another aspect of this process is that, if desired, unreacted reactants, especially acrylonitrile and the water containing the catalyst, can be conducted back into the reaction system for re-use. This overall multi-stage process provides for the altogether surprisingly economical production of 3-hydroxypropionitrile, particularly because this product is formed only to some extent during the first step of the process, yet is obtained in high yield after the penultimate (pyrolysis) step.
The claimed process includes (a) reacting acrylonitrile with water at a defined molar ratio in the presence of a weak base under specific temperature and pressure conditions until a conversion in the range of about 40% to about 80% has been achieved; (b) after cooling the mixture obtained in (a), separating off its aqueous phase; (c) distilling off the acrylonitrile from the organic phase remaining after (b); (d) subjecting the mixture obtained in (c) to pyrolysis at specific temperature and pressure conditions in the presence of a basic catalyst to obtain a mixture consisting mainly of 3-hydroxypropionitrile and acrylonitrile; and (e) isolating the desired 3-hydroxypropionitrile by fractional distillation from the mixture obtained in (d). Such a process in which the basic aqueous phase and the acrylonitrile that has been distilled off are recycled represents a preferred embodiment.
One embodiment of the invention is a process for producing 3-hydroxypropionitrile. This process includes (a) reacting acrylonitrile with water at a molar ratio of about 1:0.5 to about 1:20 in the presence of a weak base at a temperature of about 80xc2x0 C. to about 150xc2x0 C. and at a pressure of about 1 bar (0.1 MPa) to about S bar (0.5 MPa) to form a two-phase organic-aqueous mixture and until a conversion of the acrylonitrile and water to 3-hydroxypropionitrile of about 40% to about 80% is achieved, wherein the organic phase consists essentially of bis(cyanoethyl)ether, 3-hydroxypropionitrile and unreacted acrylonitrile, and the aqueous phase consists essentially of an aqueous solution of the weak base; (b) cooling the mixture obtained in (a) and separating the aqueous phase from the organic phase; (c) distilling off the acrylonitrile from the organic phase remaining after (b) to obtain a mixture consisting essentially of bis(cyanoethyl)ether and 3-hydroxypropionitrile; (d) heating the mixture obtained in (c) to a temperature of about 120xc2x0 C. to about 160xc2x0 C. at a pressure of about 5 mbar (0.5 kPa) to about 500 mbar (50 kPa) in the presence of a basic catalyst selected from the group consisting of calcium, magnesium, strontium, titanium, iron and zinc oxides, alkali metal acetates, alkali metal formates, alkali metal and barium carbonates, alkali metal bicarbonates, calcium and copper hydroxides, di- and trisodium phosphates, sodium fluoride, sodium silicate and high boiling trialkylamines, to form a mixture consisting essentially of 3-hydroxypropionitrile and acrylonitrile; and (e) isolating the 3-hydroxypropionitrile by fractional distillation from the mixture obtained in (d).
Another embodiment of the invention is a process for the production of 3-hydroxypropionitrile. This process includes (axe2x80x2) reacting acrylonitrile with water at a molar ratio of about 1:0.5 to about 1:20 in the presence of a weak base at a temperature of about 80xc2x0 C. to about 150xc2x0 C. and at a pressure of about 1 bar (0.1 MPa) to about 5 bar (0.5 MPa) to form a two-phase organic-aqueous mixture and until a conversion of the acrylonitrile and water to 3-hydroxypropionitrile of about 40% to about 80% is achieved, wherein the organic phase consists essentially of bis(cyanoethyl)ether, 3-hydroxypropionitrile, and unreacted acrylonitrile, and the aqueous phase consists essentially of an aqueous solution of the weak base; (bxe2x80x2) cooling the mixture obtained in (axe2x80x2) and neutralizing the weak base by adding a weak acid to the cooled mixture; (cxe2x80x2) distilling off the acrylonitrile and the water from the mixture obtained in (bxe2x80x2) to obtain a mixture consisting essentially of bis(cyanoethyl)ether, 3-hydroxypropionitrile, and a base formed by the neutralization; (dxe2x80x2) heating the mixture obtained in (cxe2x80x2) to a temperature of about 120xc2x0 C. to about 160xc2x0 C. at a pressure of about 5 mbar (0.5 kPa) to about 500 mbar (50 kPa) in the presence of a base formed by the neutralization in step (bxe2x80x2) to obtain a mixture consisting essentially of 3-hydroxypropionitrile and acrylonitrile; and (exe2x80x2) isolating the desired 3-hydroxypropionitrile by fractional distillation from the mixture obtained in (dxe2x80x2).
The process in accordance with the invention for the production of 3-hydroxypropionitrile is a process that starts from acrylonitrile and water, and includes (a) reacting acrylonitrile with water in a molar ratio of about 1:0.5 to about 1:20 in the presence of a weak base in a temperature range of about 80xc2x0 C. to about 150xc2x0 C. and at a pressure of about 1 bar (0.1 MPa) to about 5 bar (0.5 MPa) until a conversion in the range of about 40% to about 80% has been achieved, such that a two-phase organic-aqueous mixture is obtained, wherein the organic phase consists essentially of bis(cyanoethyl)ether, 3-hydroxypropionitrile and unreacted acrylonitrile, and the aqueous phase consists essentially of an aqueous solution of the weak base; (b) cooling the mixture obtained in (a) and separating off its aqueous phase; (c) distilling off the acrylonitrile from the organic phase remaining after (b) in order to obtain a mixture consisting essentially of bis(cyanoethyl)ether and 3-hydroxypropionitrile; (d) subjecting the mixture obtained in (c) to pyrolysis at a temperature range of about 120xc2x0 C. to about 160xc2x0 C. and at a reduced pressure of about 5 mbar (0.5 kPa) to about 500 mbar (50 kPa) in the presence of a basic catalyst selected from calcium, magnesium, strontium, titanium, iron and zinc oxides, alkali metal acetates, alkali metal formates, alkali metal and barium carbonates, alkali metal bicarbonates, calcium and copper hydroxides, di- and trisodium phosphates, sodium fluoride, sodium silicate and high boiling trialkylamines in order to obtain a mixture consisting essentially of 3-hydroxypropionitrile and acrylonitrile; and (e) isolating the desired 3-hydroxypropionitrile by fractional distillation from the mixture obtained in (d).
If desired, and even preferably, the aqueous phase separated in process step (b), which contains the majority of the base used in step (a), is conducted back into step (a) of a continuously operated overall process in order to react at step (a) with further acrylonitrile. Likewise, if desired and preferably, the acrylonitrile distilled off in process step (c) and/or in process step (e) is conducted back into step (a) of such process. A process of this kind, which features such recyclization of the basic aqueous phase, as well as of the distilled-off acrylonitrile, is presented schematically as follows: 
As used herein, the term xe2x80x9cweak basexe2x80x9d in process step (a) denotes an inorganic or organic base, the pKa value of which is about 8 to about 12. The inorganic base is preferably an alkali metal carbonate (e.g. sodium or potassium carbonate), an alkali metal bicarbonate, (e.g. sodium or potassium bicarbonate), or a mixture of two or more of these inorganic bases, (e.g. a mixture of sodium carbonate and sodium bicarbonate), and the organic base is preferably a lower trialkylamine or a 4-dialkylaminopyridine. Not only in the case of xe2x80x9clower trialkylaminexe2x80x9d, but also in the case of xe2x80x9c4-dialkylamino-pyridinexe2x80x9d, the term xe2x80x9calkylxe2x80x9d denotes preferably a C1-6-alkyl group. Examples of lower trialkylamines and 4-dialkylamino-pyridines are triethylamine and ethyldiisopropylamine, and 4-dimethylamino-pyridine, respectively. Sodium carbonate, potassium carbonate, a mixture of sodium carbonate and sodium bicarbonate or a mixture of potassium carbonate and potassium bicarbonate is preferably used as the weak base.
The amount of weak base employed is conveniently about 0.1 to about 5 mol. %, preferably about 0.5 to about 2 mol. %, based on the amount of acrylonitrile employed. The reaction of the acrylonitrile with the water is effected in process step (a) generally at a temperature of about 80xc2x0 C. to about 150xc2x0 C., preferably at temperatures in the range of about 100xc2x0 C. to about 130xc2x0 C., and generally at a pressure of about 1 bar (0.1 MPa) to about 5 bar (0.5 MPa), preferably at about 1 bar (0.1 MPa) to about 3 bar (0.3 MPa).
The acrylonitrile:water molar ratio is generally about 1:0.5 to about 1:20, preferably about 1:3 to about 1:8, particularly about 1:2 to about 1:4.
The expression xe2x80x9cwherein the organic phase consists essentially of bis(cyanoethyl)ether, 3-hydroxypropionitrile and unreacted acrylonitrilexe2x80x9d occurring in the definition of process step (a) means that the three mentioned components amount to at least 90% by weight of the organic phase. The further expression xe2x80x9cthe aqueous phase consists essentially of an aqueous solution of the weak basexe2x80x9d means that the weak base and the water in which it is dissolved amount to at least 70% by weight of the aqueous phase.
The reaction (condensation) of acrylonitrile with water in the presence of the weak base is conveniently effected on an industrial scale by combining the acrylonitrile with a solution of the base in water at room temperature in an autoclave, and heating the two-phase mixture while stirring. Pressure, which amounts to about 1 to 5 bar (0.1 to 0.5 MPa) depending on the temperature (80xc2x0 C. to 150xc2x0 C.), thereby develops in the closed autoclave.
In process step (a), the conversion is intentionally limited to the range of about 40% to about 80%, because a too high conversion leads to excessive production of undesired polymeric byproducts, as well as an increase of undesired acrylamide byproduct. The fact that unreacted acrylonitrile is present in the product is not problematical, because this starting material can be readily recovered in process step (c) and recycled, especially in step (a). Moreover, it is irrelevant whether the ratio of the products bis(cyanoethyl)ether: 3-hydroxypropionitrile in the condensation is large or small because the former product can be readily converted in process step (d) into the desired 3-hydroxypropionitrile, and the latter product is stable under the process conditions in accordance with the invention, especially the pyrolysis conditions of step (d), so that the mixture consisting mainly of the two named products can be subjected directly to pyrolysis.
Limiting the conversion necessitates the control and measurement of conversion, which can be effected conveniently by gas chromatography.
As a rule, process step (a) is completed after about 1 to 2 hours.
The advantage, in the case of step (a), of the overall process in accordance with the invention is, inter alia, the considerable suppression of the formation of undesired polymeric byproducts as well as of the likewise undesired byproduct acrylamide.
In process step (b), the separation of the aqueous phase from the two-phase organic-aqueous mixture obtained in process step (a) is accomplished. Prior to the separation, this mixture is conveniently cooled to a temperature in the range of room temperature to about +10xc2x0 C., which is effected either without active cooling or by cooling with cold water, for example water at about +5xc2x0 C. The two phases separate very readily in this temperature range.
The aqueous phase, which contains the major part of the weak base used as the catalyst, can subsequently be separated, which is conveniently effected according to methods known per se.
Preferably, the thus-separated aqueous phase, after possible replenishment with weak base, is subsequently conducted back into step (a) for reaction with additional acrylonitrile, which can also be partially recycled in a second or further cycle of process step (a).
The organic phase, which consists mainly of bis(cyanoethyl)ether, 3-hydroxypropionitrile and unreacted acrylonitrile, remaining after process step (b) has been effected, is then distilled in process step (c) in order to separate the acrylonitrile from the bis(cyanoethyl)ether and 3-hydroxypropionitrile. This is conveniently carried out by distilling off the acrylonitrile, still containing, to some extent, dissolved water, over a distillation column (e.g. a mirrored packed column), at temperatures in the range of about 60xc2x0 C. to about 100xc2x0 C. and at a pressure of about 200 mbar (20 kPa) to about 10 mbar (1 kPa). Thereby, the acrylonitrile that is distilled off is collected continuously in a suitable cooled receiver. The mixture obtained in process step (c) is a mixture consisting essentially of bis(cyanoethyl)ether and 3-hydroxypropionitril. The expression xe2x80x9cessentiallyxe2x80x9d in this context means that the two mentioned components amount to at least 80% by weight of the mixture.
The thus-separated acrylonitrile, after possible replenishment with additional acrylonitrile is preferably conducted back into step (a) for reaction with water in the presence of a weak base in a second or further cycle of process step (a).
The mixture of (essentially) bis(cyanoethyl)ether and 3-hydroxypropionitrile remaining after process step (c) has been effected is subsequently pyrolyzed in step (d), in which the bis(cyanoethyl)ether is cleaved under basic catalysis into 3-hydroxypropionitrile and acrylonitrile. This reaction occurs without the 3-hydroxypropionitrile, that is likewise present in the mixture itself, reacting. Thus, it is a surprising advantage of the process in accordance with the invention that the desired product remains unchanged under these pyrolysis conditions.
As used herein, the term xe2x80x9calkali metalxe2x80x9d in process step (d), signifies in each case lithium, sodium or potassium. When a high boiling trialkylamine is used as the basic catalyst, this refers to a trialkylamine with a boiling point at normal pressure that is higher than about 150xc2x0 C.; examples are trioctylamine and tridodecylamine.
Calcium oxide, magnesium oxide, the alkali metal acetates, the alkali metal formates, the alkali metal carbonates, barium carbonate, the alkali metal bicarbonates, calcium hydroxide, trisodium phosphate as well as sodium fluoride are preferred among the basic catalysts that can be used. Calcium oxide, sodium acetate and potassium acetate are especially preferred basic catalysts.
The amount of basic catalyst employed, which is based on the total amount of the mixture of bis(cyanoethyl)ether and 3-hydroxypropionitrile obtained in process step (c) and used in process step (d), is conveniently about 0.05 to about 10 weight percent, preferably about 0.1 to about 3 weight percent.
The pyrolysis of process step (d) is effected generally in the temperature range of about 120xc2x0 C. to about 160xc2x0 C., preferably at temperatures in the range of about 130xc2x0 C. to about 150xc2x0 C., and generally at a reduced pressure of about 5 mbar (0.5 kPa) to about 500 mbar (50 kPa), preferably at about 10 mbar (1 kPa) to about 400 mbar (40 kPa).
A mixture consisting essentially of 3-hydroxypropionitrile and acrylonitrile in the molar ratio of about 1:1 results from the pyrolysis. The duration of the pyrolysis by which such a mixture is obtained depends on the batch size and, as a rule, amounts to at least one hour. Thereby, only very small amounts of acrylamide and polymeric products are produced as byproducts, which is a further advantage of the process in accordance with the invention.
The expression xe2x80x9cmixture consisting essentially of 3-hydroxypropionitrile and acrylonitrilexe2x80x9d occurring in the previous paragraph and in the definition of process step (d) means that the two mentioned components amount to at least 90% by weight of the mixture.
The pyrolysis can be effected on an industrial scale by continuously distilling off the 3-hydroxypropionitrile and acrylonitrile products formed using a distillation column and collecting them in a cooled receiver simultaneously with pyrolysis. Alternatively, the distillation effected simultaneously with the pyrolysis can be carried out selectively by condensing the two products individually, first the 3-hydroxypropionitrile and then the acrylonitrile, by suitable cooling. In this manner, the fractional distillation of process step (e) is effectively advanced by a combination of process steps (d) and (e). This represents a modification of the process in accordance with the invention.
When the mixture of 3-hydroxypropionitrile and acrylonitrile has been obtained in process step (d), the desired 3-hydroxypropionitrile is isolated by fractional distillation in the last process step, (e). If desired, and preferably, the acrylonitrile which is thereby obtained is conducted back into step (a), and re-used analogously to the situation which is described above in connection with the performance of the earlier step (c).
The fractional distillation in accordance with process step (e) is conveniently effected initially at a bath temperature of about 50xc2x0 C. to about 120xc2x0 C. and a pressure of about 180 mbar (18 kPa) to about 10 mbar (1 kPa), whereby the majority of the acrylonitrile is distilled off, and thereafter at a bath temperature of about 120xc2x0 C. to about 150xc2x0 C. and a pressure of about 110 mbar (1 kPa) and below, whereby the majority of the desired 3-hydroxypropionitrile [boiling point about 99-102xc2x0 C./10 mbar (1 kPa)] is obtained. A mirrored packed column can be used, for example, as the distillation column.
In this manner 3-hydroxypropionitrile is obtained in very good purity and in a yield which normally amounts to more than 85%, under optimal conditions more than 90%, based on the amount of the original acrylonitrile [in process step (a)] consumed.
A further aspect of the present invention includes, after achieving the about 40% to 80% conversion in process step (a), neutralizing the weak base by the addition of a weak acid in order to obtain a two-phase organic-aqueous mixture, which instead of the original weak base contains, inter alia, the base formed by the neutralization. This base constitutes the basic catalyst used in the later process step (d), so that the addition of a basic catalyst for process step (d) is avoided.
The overall process in accordance with this aspect of the present invention includes:
(axe2x80x2) reacting acrylonitrile with water at a molar ratio of about 1:0.5 to about 1:20, in the presence of a weak base, at a temperature of about 80xc2x0 C. to about 150xc2x0 C. and at a pressure of about 1 bar (0.1 MPa) to about 5 bar (0.5 MPa), until a conversion in the range of about 40% to about 80% has been achieved in order to obtain a two-phase organic-aqueous mixture, the organic phase of which consists essentially of bis(cyanoethyl)ether, 3-hydroxypropionitrile and unreacted acrylonitrile, and the aqueous phase of which consists essentially of an aqueous solution of the weak base; (bxe2x80x2) cooling the mixture obtained in (axe2x80x2) and neutralizing the weak base by the addition of a weak acid; (cxe2x80x2) distilling off the acrylonitrile and the water from the mixture obtained in (bxe2x80x2) in order to obtain a mixture consisting essentially of bis(cyanoethyl)ether, 3-hydroxypropionitrile and the base formed by the neutralization; (dxe2x80x2) subjecting the mixture obtained in (cxe2x80x2) to pyrolysis at a temperature of about 120xc2x0 C. to about 160xc2x0 C. and at a reduced pressure of about 5 mbar (0.5 kPa) to about 500 mbar (50 kPa) in the presence of the already present base, formed by neutralization, in order to obtain a mixture consisting essentially of 3-hydroxypropionitrile and acrylonitrile; and (exe2x80x2) isolating the desired 3-hydroxypropionitrile by, for example, fractional distillation, from the mixture obtained in (dxe2x80x2).
Also in this process, if desired, and even preferably, the acrylonitrile distilled off in process step (cxe2x80x2) and/or in process step (exe2x80x2) is conducted back into step (axe2x80x2) of a continuously operated overall process in accordance with this aspect of the invention.
The conditions of process steps (axe2x80x2), (cxe2x80x2), (dxe2x80x2) and (exe2x80x2) correspond in general to those conditions which are described above in connection with process steps (a), (c), (d) and (e), respectively. This also applies to process step (cxe2x80x2) vis-à-vis process step (c), although in the former step not only acrylonitrile but also water are distilled off, and also to process step (dxe2x80x2) vis-à-vis process step (d), although in the former step the base which serves as the basic catalyst is already present in the mixture of bis(cyanoethyl)ether and acrylonitrile after carrying out process step (cxe2x80x2). Furthermore, the expressions xe2x80x9cconsists essentially ofxe2x80x9d occurring in the above definition of process step (axe2x80x2), xe2x80x9cconsisting essentially ofxe2x80x9d occurring in the above definition of process step (cxe2x80x2), and xe2x80x9cconsisting essentially ofxe2x80x9d occurring in the above definition of process step (dxe2x80x2) have the same meanings as given hereinabove in relation to the process steps (a), (c) and (d) of the first mentioned embodiment or aspect of the present invention, i.e. at least 90%, at least 70%, at least 80% and at least 90%, in each case by weight, respectively.
As the weak acid, which is used for the neutralization of the weak base in process step (bxe2x80x2), there is especially used a lower (C1-3) carboxylic acid, (e.g. formic acid, acetic acid or propionic acid). For example, when sodium carbonate or sodium bicarbonate is used as the weak base and acetic acid is used as the weak acid, the base sodium acetate is formed by the neutralization. Preferably, a mixture of sodium carbonate and sodium bicarbonate is used as the weak base and acetic acid is used as the weak acid in the process in accordance with this aspect of the present invention.
If desired, the 3-hydroxypropionitrile obtained can be subjected to a hydrogenation to give 3-aminopropanol. Methods known per se can be used for this purpose, for example, using Raney nickel as the catalyst in methanol or ethanol and in the presence of anhydrous ammonia, as described in, for example, Swiss Patent No. 244,837, and J. Chem. Soc. 1946, 94, as well as JP Kokai No. 9963/1989. Ammonia prevents to a large extent the formation of secondary amines. The hydrogenation is conveniently effected at temperatures of about 100xc2x0 C. and at pressures of about 25 to about 100 bar H2 (about 2.5 to about 10.0 MPa).
The following examples are provided to further illustrate the process of the present invention. These examples are illustrative only and are not intended to limit the scope of the invention in any way.